In amplifier systems for musical instruments such as quitars or the like, most present day guitar preamplifier circuits utilize a variable feedback type circuit. The advantages of such a variable feedback type circuit include relatively wide dynamic range (more than 3 volts RMS for input overload), high input impedance, and good noise.
At normal guitar settings (12:00), the overall low frequency (L.F.) gain is approximately 18, and the high frequency gain (H.F.) is approximately 120. This high frequency boost is needed to properly equalize a guitar system (primarily speaker roll-off and the guitar system itself). Contemporary music now dictates a good front end overload condition which is accomplished by operating the volume at a maximum setting ("10") and by controlling the level with a post volume control. The resulting gains at such maximum volume setting are a L.F. gain of approximately 240 and a H.F. gain of approximately 1,600.
Generally a gain of at least 200 is required for smooth distortion effects but the excessive high frequency boost referred to above is not needed and usually causes intense high frequency oscillations and instability, as well as making the sound quality harsh or sharp sounding. Obviously a system which would reduce the high frequency boost at high volume settings would be desirable.